Vacuum tube assembly process



Aug. 8, 1950 B. R. CORSON VACUUM TUBE ASSEMBLY PROCESS Filed Jan. 5, 1949 H Rn 60 m HN 5 6F. .r WWW. w r- NC Patented Aug. 8, 1950 2,517,981 VACUUM TUBE ASSEMBLY raoonss Bayard R. Corson, Fishkill, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application January 5, 1949, Serial No. 69,254

4 Claims.

This invention pertains to the assembly and manufacture of vacuum tubes and similar electronics devices. v

Vacuum tubes having multi-grid structures are well known and are currently manufactured in large quantities. Normally certain rather exacting tolerances are specified in these devices, the departure from which rendering the device unsuited for use. Among other requirements is found the necessity for proper grid inter-alignment relative to the various grids and the parts thereof. For example, where grids are wound. it is essential that the lateral wires of each grid are maintained in proper spaced relationship with respect to the lateral wires of the other grids in the tube, frequently the alignment tolerance be- 1 8 of the order of a few thousandths of an inch. In common assembly practice this alignment is performed visually by the assembly operator, with or without an optical aid, when the tube elements are assembled to the base stem or the spacing washers. Normally, the grids are wound of a nickel wire or a similar metallic wire, and since the appearance of each winding is substantially the same, it is not only difllcult for the operator to distinguish between the several windings under assembly, but also impracticable for him to assemble the grids with great accuracy, relative to the inter-alignment of their turns, without a considerable amount of time being consumed upon each tube.

It has been determined that in the assembly of certain standard types of multi-grid vacuum tubes the single operation requiring the longest time is the operation of aligning the grids. This operation is evenmore significant in'the consumption of assembly time where special purpose tubes are manufactured requiring very much closer alignment tolerances. Tubes with poor alignment tolerance frequently have high screen grid current in operation, and many such tubes are rejected solely for that reason on final test. Production costs, therefore, invariably are affected adversely unless the necessary precision in grid inter-alignment is properly maintained in assembly and manufacture.

While certain grid aligning equipment has been developed. it is frequently unsatisfactory due to its unwieldiness and the need for frequent readjustments of the apparatus. In the present invention, on the other hand, a simple process has been developed wherein each type grid is dyed a different contrasting color before assembly so that the assembly operator may by visual determination more effectively perform the necessary alignment during assembly. Since retention of the dye material upon the grids of the tube after assembly is undesirable because of the reduction of electron flow control afforded thereby, and for other operating reasons, the present invention includes a further step in the manufacturing process wherein the dyes are removed from the grid wires during the normal firing and evacuation process.

A primary object of this invention is, therefore, to provide a process wherein the grid element inter-alignment of a vacuum tube under assembly is accurately, readily, and economically performed. 1 Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle. In the drawings:

Fig. 1 is a diagrammatic view of a wire wound grid element.

Fig. 2 shows in diagram a simple means where-- 3 grids after being wound may be dyed and Fig. 3 illustrates in diagram a grid structure of a vacuum tube having three different grids and further illustrates the problem out of which the present invention materialized.

Fig. 4 shows a vacuum tube being fired and evacuated, and is illustrative of standard practice in the manufacture of such devices.

Referring briefly to Fig. 1, a grid structure comprising the support rods. i0 and II and a helical winding l2, crimped or welded to the rods is shown. This type of grid is commonly used in the numerous receiving type vacuum tubes, and may be circular or elliptical in cross-section. Normally, in carrying out the invention several diilerent sizes of grids are so constructed, corresponding respectively, for example, to the control grid, screen grid, and suppressor grid of a conventional pentode type vacuum tube.

Now referring to Fig. 2 each different type grid is dyed in the receptacles l3, H, and II. For example, receptacle I3 may contain a r dye, receptacle I 4 a "brown" dye, and receptacle II a "green" dye. While no part of the present invention, the composition of the dye is material in affecting the result to be obtained. Essentially the dye must be a liquid having adhesive qualities sufllcient to color the metals of which the grids are composed. In addition, the dye must be such that it will volatilize at reasonably high temperatures.

Suitable dyes may b prepared from standard neutral dyes mixed with nitro cellulose or with ethyl cellulose. A typical dye may be prepared to give a red color from toluylene red and nitro cellulose.

After each grid is dipped into its dye bath in the aforementioned receptacles, it is dried upon a rack l6 so that in the embodiment herein related, the grid I1 is dyed brown," the grid l8 green, and the grid [9 red.

Referring to Fig. 3, the various grids are assembled between a pair of washers'20 and 2| through which the grid support rods project. Since each grid is colored with a distinctly contrasting dye, it is obvious that an assembly operator may readily discern the alignment and accordingly adjust the assembly as required. After the grid assembly is properly adjusted it is assembled with the other vacuum tube elements (cathode and anode) and placed into an appropriate envelope 22, sealed to an exhaust stem 23, and prepared for firing and evacuating in a conventional manner similar to that illustrated by Fig. 4.

In Fig. 4 a tube 24 leads to an evacuating pump 28 whereby the gases within the envelope 22 are exhausted. The envelope 22 is additionally provided with a surrounding induction coil 26 which is connected to a suitable source of high frequency via the lines 21 whereby metallic elements, including the grids l1, l8, and i9 within the envelope 22 are inductively heated together with a getter 29. Since the dye chosen to cover the grid wires is capable of volatilizing under the temperature to which the grids are thus subjected, the dyes on the various grids thereby volatilize and the products therefrom are drawn oil with the other gases within the envelope 22 by the pump 25.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the apparatus illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. In the manufacture of a multi-grid vacuum tube the method of assembling the grid members thereof to have a predetermined inter-alignment of their respective elements comprising the steps of, dyeing the elements of each said member a different color, aligning the elements of'the respective grids with the aid of the color contrast so obtained, sealing the assembly into a suitable envelope, volatilizing the said dyes covering each grid by generating heat therein, and evacuating the products of volatilization from the envelope.

2. In the manufacture of a vacuum tube device having a plurality of nested, wire-wound grids, the method of securing accurate assembly inter-alignment between spaced turns of the respective grids consisting Of the steps of dyeing the turns of each grid a different color, assembling the grids to have proper alignment between the said turns determined from their color contrast, heating the said grids for removing the dye therefrom, and evacuating the resulting gases from the said device.

3. In the manufacture of a vacuum tube device having a plurality of similar alignable elements, the method of providing accurate assembly interalignment therebetween comprising the steps of immersing each different element in a different colored bath of volatile dye, drying the said elements, visually aligning the said elements and thereafter fixing the said alignment by means of their color contrast, and causing the said dyes to be volatilized and the products therefrom removed during the firing and evacuating of the said device.

4. In the process of manufacturing a vacuum tube device wherein the final step consists of firing and evacuating the envelope enclosing the said device, the said device having a plurality of concentric, wire-wound grids, the steps of tinting the wires of each grid a different contrasting color with a heat-vaporizable dye, aligning the said wires of the respective grids relative to each other by visual observation of the color contrast therebetween, and vaporizing the said dyes during the said firing and evacuating step.

BAYARD R. CORSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,716,159 Widell June 4, 1929 2,229,436 Beggs Jan. 21, 1941 2,247,688 Kinyon July 1, 1941 2,417,730 Becker Mar. 18, 1947 

